The Ball In and Out of Play is the ninth law of the Laws of the Game of football (soccer), and describes to the two basic states of play in the game.

Out of play
When the ball has left the field of play or play has been stopped by the referee, it becomes out of play until play is recommenced by the appropriate restart.
When the ball is out of play the ball is "dead"; players must not play the ball or interfere with their opponents, and goals can not be scored.
By definition, fouls do not occur when the ball is out of play, however misconduct may occur.
Substitutions may only be made when the ball is out of play (and then only with the permission of the referee).